Switched-mode power supplies and motor drives often use half-bridge or full-bridge switching topologies to transfer energy from an input supply to a regulated output node. A half-bridge topology includes, for example, two switches that are connected in a totem pole configuration, while a full-bridge includes two half-bridge circuits coupled in parallel. A gate driver circuit is used to drive the each of the switches in the half-bridge configuration.
In various switched-mode power supply applications, a low side gate driver and a high side gate driver circuit may be used to control a low side switch and a high side switch respectively in the half-bridge. The low side switch is often referenced to a ground voltage and the low side gate driver circuit is designed to generate a gate control signal that is also referenced to the ground voltage. The high side driver, on the other hand, may not be referenced to ground and may use bootstrapped power supply techniques in order to supply power to the high side switch. One such bootstrap technique involves using a bootstrap capacitor to effectively create a local floating power supply for the high side switch driver that is referenced to a node of the high side switch. During each switching cycle, the bootstrap capacitor provides energy to the high side switch driver and then is recharged via a diode that is connected to the low side switch. In typical systems, additional level shifting circuits are used to activate the high side switch driver with ground referenced logic signals.